import java.util.Arrays;

public class MyStack {

    public int[] elem;
    public int usedSize;

    public MyStack() {
        this.elem = new int[2];
    }

    public void push(int val) {
        if(isFull()) {
            this.elem = Arrays.copyOf(elem,2*elem.length);
        }
        elem[usedSize] = val;
        usedSize++;
    }

    public boolean isFull() {
        return usedSize == elem.length;
    }

    public int pop() {
        if(isEmpty()) {
            return -1;
        }
        int ret = elem[usedSize-1];
        usedSize--;
        return ret;
    }
    public boolean isEmpty() {
        return usedSize == 0;
    }

    public int peek() {
        if(isEmpty()) {
            return -1;
        }
        return elem[usedSize-1];
    }

    public int size() {
        return usedSize;
    }

}